/Engine/Plugins/Runtime/MIDIDevice/Source/MIDIDevice/Public/MIDIDeviceManager.h
Enumerates all of the MIDI input and output devices and reports back useful infos such as IDs and names of those devices. This operation is a little expensive so only do it once at startup, or if you think that a new device may have been connected.
[UFUNCTION](Programming/UnrealArchitecture/Reference/Functions)(BlueprintCallable, Category="MIDI Device Manager") static void FindAllMIDIDeviceInfo ( [TArray](API\Runtime\Core\Containers\TArray)< [FMIDIDeviceInfo](API\Plugins\MIDIDevice\FMIDIDeviceInfo) > & OutMIDIInputDevices, [TArray](API\Runtime\Core\Containers\TArray)< [FMIDIDeviceInfo](API\Plugins\MIDIDevice\FMIDIDeviceInfo) > & OutMIDIOutputDevices )